Implantable electrical tissue stimulating devices are well known in the art. For example, one of the betterknown tissue stimulators is the cardiac pacer, as shown, for example, in U.S. Pat. No. 3,057,356 to Wilson Greatbatch. These devices, such as the cardiac pacer, generally comprise a pulse generator further comprising a power source (battery) and associated electrical circuitry embedded in, and encapsulated in, or protected by a substance or substances substantially inert to body fluids and tissue. The electrical circuitry of the pulse generator is adapted to be connected by a lead or leads to one or more electrodes which are adapted to be placed adjacent to a remote, desired spot within the human body, such as adjacent to or within myocardial tissue. The cardiac pacer, for example, supplies electrical stimulating pulses to regulate cardiac function in the absence of naturally occurring cardiac pulses.
In implantation of pulse generator and lead, it is common practice for the surgeon to surgically attach or place the electrode distal end of the lead at the desired spot within the human body, that is, in or adjacent to myocardial tissue, and to thereafter connect the lead to a connector assembly associated with the electrical circuitry of the pulse generator in order to commence electrical stimulation of the heart tissue. Prior to making the electrical connection, the surgeon usually measures the electrical stimulation threshold level sufficient to maintain capture of the heart and the sensing threshold level sufficient to trigger the sense amplifier, if any, in the pulse generator circuitry to inhibit the generation of electrical stimulating pulses in the event the heart is functioning normally.
Thereafter, if the threshold levels are adequate, the surgeon usually creates a subcutaneous pocket to receive the encapsulated pulse generator in connective tissue lying just beneath the skin. After the pulse generator is slipped into the pocket, the incision is closed and precautions are taken to avoid build-up of inert body fluids in the pocket and to guard against infections.
At the time of manufacture of the device, the electrical circuitry, including the connector assembly, is connected to the power source. From the time of manufacture of the unit, therefor, current is drawn from the power source through the connector assembly and the unit immediately commences its useful life of from three to five years at the present time. In some instances, the unit may be stored for a period of a year or so before implantation, reducing its implantation life by as much as one-third.
While there are perhaps many approaches which might come to mind to alleviate this shelf degradation problem, it must be kept in mind that any such solution must not entail substantial change in the manner of handling the unit by the surgeon. Surgeons have become accustomed to the rather simple above-described implantation technique and experience has shown them to be resistant to changes in routine for a variety of reasons. Thus, while theoretically possible to provide the units in a dissembled state, e.g., this would require final assembly by the surgeon or others at or near the time of implantation. Thus, assembly would be placed in the hands of those other than the manufacturer's employees who are highly skilled in such procedures. Nor must any solution to the problem entail a nonconventional manipulative procedure foreign to the surgeons past modus operandi lest the procedure be mishandled or perhaps forgotten. It is to be appreciated, of course, that in any surgical procedure additional demands placed on the surgeon or his team are to be avoided if at all possible.
In this context, it is an object of the present invention to provide a tissue stimulating device having an extended useful implantation life.
A further object is to provide a tissue stimulating device wherein power is not dissipated from the power source until the time of implantation.
Another object is a device of the foregoing type which does not entail any change in handling procedures by the operating team.